Every time I've looked at something like that, it just hasn't been worth the hassle, and hasn't been economically competitive with getting a dedicated server on

Every time I've looked at something like that, it just hasn't been worth the hassle, and hasn't been economically competitive with getting a dedicated server on Hetzner or Hetzner auction. Those boat anchor servers on ebay will be WAY slower than a modern threadripper. Or if you only need a few hours at a time, Hetzner cloud is competitive without having to worry about preemption.